In recent years, there has been a trend in development towards supercharged engines, wherein the economic significance of the engines for the automobile industry continues to steadily increase.
Supercharging is primarily a method for increasing performance in which the air required for the combustion process in the engine is compressed, as a result of which a greater air mass can be fed to each cylinder in each working cycle. In this way, the fuel mass and therefore the mean pressure can be increased.
Supercharging is a suitable means for increasing the power of an internal combustion engine while maintaining an unchanged swept volume, or for reducing the swept volume while maintaining the same power. In any case, supercharging leads to an increase in volumetric power output and a more expedient power-to-weight ratio. If the swept volume is reduced, it is thus possible to shift the load collective toward higher loads, at which the specific fuel consumption is lower. By means of supercharging in combination with a suitable transmission configuration, it is also possible to realize so-called downspeeding, with which it is likewise possible to achieve a lower specific fuel consumption.
Supercharging consequently assists in the constant efforts in the development of internal combustion engines to minimize fuel consumption, that is to say to improve the efficiency of the internal combustion engine.
For supercharging, use is often made of an exhaust-gas turbocharger, in which a compressor and a turbine are arranged on the same shaft. The hot exhaust-gas flow is fed to the turbine and expands in the turbine with a release of energy, as a result of which the shaft is set in rotation. The energy supplied by the exhaust-gas flow to the turbine and ultimately to the shaft is used for driving the compressor which is likewise arranged on the shaft. The compressor conveys and compresses the charge air fed to it, as a result of which supercharging of the cylinders is obtained. A charge-air cooler is advantageously provided in the intake system downstream of the compressor, by means of which charge-air cooler the compressed charge air is cooled before it enters the at least one cylinder. The cooler lowers the temperature and thereby increases the density of the charge air, such that the cooler also contributes to improved charging of the cylinders, that is to say to a greater air mass. Compression by cooling takes place.
The advantage of an exhaust-gas turbocharger in relation to a mechanical supercharger consists in that an exhaust-gas turbocharger utilizes the exhaust-gas energy of the hot exhaust gases, whereas a mechanical supercharger draws the energy required for driving it directly or indirectly from the internal combustion engine. In general, a mechanical connection is required for the transmission of power between the supercharger and the internal combustion engine.
The advantage of a mechanical supercharger in relation to an exhaust-gas turbocharger consists in that the mechanical supercharger generates, and makes available, the required charge pressure at all times, specifically regardless of the operating state of the internal combustion engine, in particular regardless of the present rotational speed of the crankshaft. This applies in particular to a mechanical supercharger which can be driven by way of an electric machine.
In the prior art, it is specifically the case that difficulties are encountered in achieving an increase in power in all engine speed ranges by means of exhaust-gas turbocharging. A relatively severe torque drop is observed in the event of a certain engine speed being undershot. The torque drop is understandable if one takes into consideration that the charge pressure ratio is dependent on the turbine pressure ratio or the turbine power. If the engine speed is reduced, this leads to a smaller exhaust-gas mass flow and therefore to a lower turbine pressure ratio or lower turbine power. Consequently, toward lower engine speeds, the charge pressure ratio likewise decreases. This equates to a torque drop.
Attempts have been made to mitigate the problems with reduced torque in lower engine speed conditions. For example U.S. Pat. No. 6,418,719 discloses a system and method for using an engine's exhaust back pressure to control a variable geometry turbocharger. The control system determines a desired exhaust back pressure based on engine speed and engine load, and actuates turbocharger nozzles to achieve the desired exhaust back pressure.
However, the inventors herein have recognized potential issues with such systems. For example, the system appears to add a considerable level of complexity, and cost, to the engine. Embodiments in accordance with the present disclosure provide a more straightforward approach to mitigate potential torque drop during low engine speed operation.
Embodiments in accordance with the present disclosure may be directed to a supercharged internal combustion engine that may include an intake system for the supply of a charge-air flow, an exhaust-gas discharge system for the discharge of exhaust gas, and at least one blower arranged in the intake system. The blower may be equipped with at least one impeller, which may be mounted in a housing, on a rotatable shaft. The internal combustion engine may also include an exhaust-gas recirculation (EGR) arrangement comprising a recirculation line which branches off from the exhaust-gas discharge system and which opens into the intake system upstream of the at least one impeller so as to form a junction point, the recirculation line branching off upstream of a turbine arranged in the exhaust-gas discharge system. The supercharged internal combustion engine may also include a flap which may be delimited circumferentially by an edge and which may be arranged in the intake system at the junction point and which may be pivotable about an axis running transversely with respect to the fresh-air flow, in such a way that the flap, in a first end position, by way of a front side, blocks the intake system and opens up the recirculation line, and in a second end position, by way of a rear side, covers the recirculation line and opens up the intake system. Wherein the flap may not be planar, and may have, at least in the front side, at least one flow modification element, or feature, for example a deformation as, for example, an unevenness.
The invention also relates to a method for operating an internal combustion engine of the type, in which the at least one blower has an inlet region which runs, and is formed, coaxially with respect to the shaft of the at least one impeller.
An internal combustion engine of the type described herein may be used as a motor vehicle drive unit. Within the context of the present disclosure, the expression “internal combustion engine” may encompass diesel engines and Otto-cycle engines and also hybrid internal combustion engines, which utilize a hybrid combustion process, and hybrid drives which comprise not only the internal combustion engine but also an electric machine which can be connected in terms of drive to the internal combustion engine and which receives power from the internal combustion engine or which, as a switchable auxiliary drive, additionally outputs power.
The internal combustion engine may have a blower for supercharging purposes, wherein, in the context of the present disclosure, the expression “blower” may encompass both mechanical superchargers and compressors of exhaust-gas turbochargers.
It is a further basic aim to reduce pollutant emissions. Supercharging can likewise be expedient in solving this problem. With targeted configuration of the supercharging, it is possible specifically to obtain advantages with regard to efficiency and with regard to exhaust-gas emissions. To adhere to future limit values for pollutant emissions, however, further engine-internal measures are necessary in addition to the supercharging arrangement.
For example, exhaust-gas recirculation serves for reducing the untreated nitrogen oxide emissions. Here, the recirculation rate xEGR is determined as xEGR=mEGR/(mEGR+mfresh air), where mEGR denotes the mass of recirculated exhaust gas and mfresh air denotes the supplied fresh air. Any oxygen or air recirculated via the exhaust-gas recirculation arrangement can be taken into consideration.
The internal combustion engine according to the invention which may be supercharged by way of a blower may also equipped with an exhaust-gas recirculation (EGR) arrangement, wherein the recirculation line, which branches off from the exhaust-gas discharge system, opens into the intake system, so as to form a junction point, upstream of the blower, as is generally the case in a low-pressure EGR arrangement, in which exhaust gas that has already passed through a turbine arranged in the exhaust-gas discharge system is recirculated to the inlet side. For this purpose, the low-pressure EGR arrangement comprises a recirculation line which branches off from the exhaust-gas discharge system downstream of the turbine and issues into the intake system upstream of the compressor.
The internal combustion engine to which the present disclosure relates may furthermore have a flap which may be arranged in the intake system at the junction point. The flap may serve for the adjustment of the fresh-air flow rate supplied via the intake system, and at the same time for the metering of the exhaust-gas flow rate recirculated via the exhaust-gas recirculation arrangement, and may be pivotable about an axis running transversely with respect to the fresh-air flow, in such a way that, in a first end position, the front side of the flap may block the intake system, and at the same time the recirculation line is opened up, and in a second end position, the rear side of the flap may cover the recirculation line, and at the same time the intake system may be opened up. In the above context, both “blocking” and “covering” do not imperatively also mean “closing”.
The axis, running transversely with respect to the fresh-air flow, about which the flap is pivotable need not be a physical axle. Rather, the axis may be a virtual axis, the position of which in relation to the rest of the intake system may furthermore exhibit a certain play, wherein the mounting or fastening may be realized in some other way.
It is basically sought to shift the surge limit of the blower as far as possible toward smaller charge-air flows, in particular in the case of exhaust-gas turbocharging. It is then possible, even in the presence of small compressor flows, to realize high charge pressure ratios, whereby the torque characteristic in the low engine speed range may be considerably improved. The flow approaching the blower is of particular significance with regard to a shift of the surge limit.
Various embodiments may provide a supercharged internal combustion engine by means of which the disadvantages known from the prior art may be overcome and smaller charge-air flows can be realized and compressed.
Embodiments may provide a method for operating an internal combustion engine of the type, in which the at least one blower has an inlet region which runs, and may be formed, coaxially with respect to the shaft of the at least one impeller.
The flap of the internal combustion engine according to the present disclosure may not be, as in the case of a conventional internal combustion engine, of planar and plate-like form, that is to say similar to a plate, with a width and height that amount to several times the thickness. Rather, the flap according to the present disclosure may have a visibly three-dimensional form and may thus has a certain depth, wherein the depth, or the unevenness, may result from at least one deformation on the front side of the flap.
For the formation of a flap according to the present disclosure, use may even be made of an originally planar flap which may be deformed for the purposes of introducing at least one deformation. The approach may also be advantageous with regard to the retrofitting of an internal combustion engine with a flap according to the present disclosure.
Tests have shown that the deformation of the flap may have, or may give rise to, expedient effects in terms of flow. A substantially axial charge-air flow or fresh-air flow may have a speed component transverse with respect to the shaft of the blower, that is to say a swirl, forcibly imparted to it by way of the flap. In this way, the surge limit of the blower can be shifted toward smaller charge-air flows, whereby relatively high charge-pressure ratios are achieved even in the case of small charge-air flows. The torque characteristic of the supercharged internal combustion engine may be noticeably improved in the lower engine speed range.
In this way, the first object on which the present disclosure is directed may be achieved. That is to say a supercharged internal combustion engine may be provided by means of which the disadvantages known from the prior art are overcome and smaller charge-air flows can be realized and compressed.
According to the present disclosure, the recirculation line may branch off from the exhaust-gas discharge system upstream of the turbine, similarly to a high-pressure EGR arrangement.
If exhaust gas extracted from the exhaust-gas discharge system upstream of the turbine is introduced into the intake system, this duly has the effect that the exhaust-gas flow introduced into the turbine is, in the case of exhaust-gas recirculation, reduced by the recirculated exhaust-gas flow rate. On the other hand, this approach may increase the pressure gradient between the outlet side and the inlet side, as a driving force for the recirculation of preferably cooled exhaust gas. This may offer advantages in particular in the case of high recirculation rates, which may provide a greater pressure gradient.
Since the recirculated exhaust gas is introduced, and mixed with fresh air, upstream of the blower, the recirculated exhaust gas may be subjected to exhaust-gas aftertreatment, in particular in a particle filter. There is then minimal risk of depositions in the blower which may change the geometry of the blower, in particular the flow cross sections, and thereby impair the efficiency of the blower.
Embodiments of the internal combustion engine of the present disclosure may be advantageous in which the axis may be arranged close to an edge section of the flap. In this embodiment, the flap may be laterally mounted and pivotable similarly to a door, specifically at one of its edges. This may distinguish the flap according to the present disclosure from centrally mounted shut-off elements or flaps, such as for example a butterfly valve.
Embodiments of the internal combustion engine may be advantageous in which the axis may be arranged close to a wall section of the intake system. The intake system generally performs, with regard to the flap, the function of a frame, that is to say borders the flap. In this respect, an embodiment in which the axis is arranged close to an edge section of the flap may be, generally, also an embodiment in which the axis is arranged close to a wall section of the intake system. The major advantage of both embodiments may include, in the second end position, the flap may be positioned close to the wall, such that a completely free passage for the fresh air may be realized.
Embodiments of the internal combustion engine may be advantageous in which the at least one deformation of the flap comprises at least one kink. Embodiments of the internal combustion engine may also, or instead, be advantageous in particular in which the at least one deformation of the flap comprises at least one bulge. A bulge, that is to say a rounded flap surface or flap front side, may be aerodynamically more expedient, and may conduct the fresh air in the direction of the impeller with little turbulence. By contrast, a kink, that is to say a sharp rim, may give rise to pronounced turbulence in the fresh-air flow that is drawn in. This may be regarded as disadvantageous owing to the pressure loss in the fresh air that is drawn in, though may also have advantages with regard to thorough mixing of the fresh air with the recirculated exhaust gas. In some cases, the at least one bulge may be convex. In some cases, the at least one bulge may be concave.
In the two above embodiments, the front side of the flap may serve as a reference plane, that is to say the statement as to whether, in an individual case, a bulge that is provided is arched inward or outward may be made proceeding from the front side, wherein, a virtually planar front side of the flap may be taken as a starting point.
Embodiments of the internal combustion engine may be advantageous in which the at least one deformation on the front side of the flap may face toward and may oppose the fresh-air flow at least in the first end position of the flap. Then, the at least one deformation may project, as it were, into the fresh-air flow.
Embodiments of the internal combustion engine may be advantageous in which the at least one deformation may encompass an edge region of the flap situated opposite the axis, or the at least one deformation may be delimited on the edge region of the flap. This is that edge region of the flap over which the fresh-air flow passes, and across which the flow is conducted in the direction of the impeller. In this respect, the section in particular may be suitable for a guiding function or for introducing a swirl into a substantially axial fresh-air flow. The edge of the region may also be referred to as separation rim of the flap.
In this context, embodiments of the internal combustion engine may be advantageous in which the at least one deformation encompasses an edge corner region on one side of the flap, or the at least one deformation is delimited on the edge corner region of the flap. A corner of the flap according to the invention may be generally a rounded corner. Deforming the flap only on one side may make it easier for a speed component transverse with respect to the shaft of the impeller to be introduced, that is to say for a swirl to be introduced, into a substantially axial fresh-air flow. At least one deformation of the flap in the edge corner region may yield a helically twisted form.
Embodiments of the internal combustion engine may be advantageous in which at least one exhaust-gas turbocharger may be provided which comprises the turbine arranged in the exhaust-gas discharge system and a compressor arranged in the intake system. With regard to the above embodiment, reference is made to the statements already made in conjunction with the exhaust-gas turbocharging arrangement, for example to the highlighted advantages. In this context, embodiments of the internal combustion engine may also be advantageous in which the at least one blower is the compressor of the at least one exhaust-gas turbocharger.
Embodiments of the internal combustion engine may be advantageous in which the at least one blower may be a radial blower. This embodiment may permit dense packaging with regard to the supercharging arrangement. The blower housing can be configured as a spiral or worm housing. In the case of an exhaust-gas turbocharger, the diversion of the charge-air flow in the compressor of the exhaust-gas turbocharger can advantageously be utilized for conducting the compressed charge air on the shortest path from the outlet side, on which the turbine of the exhaust-gas turbocharger is commonly arranged, to the inlet side.
In this context, embodiments of the internal combustion engine may be advantageous in which the turbine is a radial turbine. This embodiment permits, for example, dense packaging of the exhaust-gas turbocharger and thus of the supercharging arrangement as a whole, if the turbine is a turbine of an exhaust-gas turbocharger.
By contrast to turbines, compressors or blowers may be defined in terms of their exit flow. A radial blower or radial compressor may thus be a blower or compressor whose flow exiting the rotor blades runs substantially radially. In the context of the present disclosure, “substantially radially” may mean that the speed component in the radial direction is greater than the axial speed component.
Embodiments of the internal combustion engine may however also be advantageous in which the blower may be of axial type of construction. The flow exiting the impeller blades of an axial blower may run substantially axially.
Embodiments of the internal combustion engine may be advantageous in which the at least one blower has an inlet region which runs coaxially with respect to the shaft of the at least one impeller and which may be designed such that the flow of charge air approaching the at least one impeller runs substantially axially.
In the case of an axial inflow to the blower or compressor, a diversion or change in direction of the charge-air flow in the intake system upstream of the at least one impeller is often omitted, whereby unnecessary pressure losses in the charge-air flow owing to flow diversion are avoided, and the pressure of the charge air at the inlet into the blower is increased. The absence of a change in direction may also reduce the contact of the exhaust gas and/or charge air with the internal wall of the intake system and/or with the internal wall of the blower housing, and thus reduces the heat transfer and the formation of condensate.
Embodiments of the internal combustion engine may be advantageous in which a shut-off element is arranged in the intake system upstream of the junction point. The shut-off element may serve, at the inlet side, for reducing the pressure in the intake system, and can thus be conducive to increasing the pressure gradient between the exhaust-gas discharge system and the intake system. In this connection, embodiments of the internal combustion engine may be advantageous in which the shut-off element is a pivotable or rotatable flap.
Embodiments of the internal combustion engine may be advantageous in which the recirculation line is equipped with a valve which comprises an axially displaceable valve body which is connected, and thereby mechanically coupled, to the flap, a pivoting of the flap causing a displacement of the valve body. Consequently, the flap can serve as an actuation device for the valve, and/or the valve can serve as an actuation device for the flap.
All variants of the above embodiments may have in common the fact that the flap serves for the setting of the air flow rate supplied via the intake system, and not for the metering of the recirculated exhaust-gas flow rate. The latter is effected by way of the valve, which may be fitted in the recirculation line and serves as an EGR valve.
Embodiments of the internal combustion engine may be advantageous in which the junction point is formed and arranged in the vicinity of, at a distance A from, the at least one impeller. An arrangement of the junction point close to the blower may shorten the path for the hot recirculated exhaust gas from the point at which it is introduced into the intake system to the at least one impeller, such that the time available for the formation of condensate droplets in the free charge-air flow may be reduced. A formation of condensate droplets is thus counteracted in this way. Furthermore, a swirl introduced into the flow using the flap remains effective, that is to say is still pronounced, at the point at which the charge air enters the impeller. This is also intended and therefore advantageous.
In this connection, embodiments of the internal combustion engine may be advantageous in which, for the spacing Δ, the following applies: Δ≤2.0DV or Δ≤1.5DV, where DV denotes the diameter of the at least one impeller. Embodiments may be advantageous in which, for the spacing Δ, the following applies: Δ≤1.0DV, preferably Δ≤0.75DV.
The second sub-object on which the present disclosure is based, for example, of specifying a method for operating a supercharged internal combustion engine of an above type, in which the at least one blower may have an inlet region which runs, and may be formed, coaxially with respect to the shaft of the at least one impeller, may be achieved by way of a method in which a substantially axial fresh-air flow has a speed component transverse with respect to the shaft of the at least one impeller forcibly imparted to it by way of the flap.
That which has already been stated with regard to the internal combustion engine according to the invention also applies to the method according to the invention, for which reason reference is generally made at this juncture to the statements made above with regard to the supercharged internal combustion engine. The different internal combustion engines require, in part, different method variants.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.